Flagellasialin: a novel sulfated  2,9-linked polysialic acid glycoprotein of sea urchin sperm flagella

Abstract

A novel alpha2,9-linked polysialic acid (polySia)-containing glycoprotein of sea urchin sperm flagella was identified and named "flagellasialin." Flagellasialin from Hemicentrotus pulcherrimus shows a diverse relative molecular mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of 40-80 kDa. Flagellasialin is a 96-amino acid, threonine-rich, heavily O-glycosylated (80-90% by weight) glycoprotein with a single transmembrane segment at its C-terminus and no apparent cytosolic domain. Of 12 extracellular Thr residues, eight are O-glycosylated and three are nonglycosylated. Flagellasialin is highly expressed in the testis but cannot be detected in the ovary. The amino acid sequences of flagellasialin from three sea urchin species (H. pulcherrimus, Strongylocentrotus purpuratus, and Strongylocentrotus franciscanus) are identical, but some species differences exist in the three core glycan structures to which the sulfated alpha2,9-linked polyNeu5Ac chain is linked. Finally, the treatment of sperm with a specific antibody against the alpha2,9-linked polyNeu5Ac structure results in the elevation of intracellular Ca(2+) and inhibition of sperm motility and fertilization, implicating flagellasialin as a regulator of these critical processes.

Sperm and Egg Jelly Coat from Sea Urchin Lytechinus variegatus Collected in Rio de Janeiro Contain Distinct Sialic Acid-Rich Polysaccharides

“…They participate in the recognition and interaction events that are essential for the growth, development and immunological reaction of these organisms (Nasirikenari et al 2006;Nacher et al 2010). Occasionally, sialic acids may be linked to each other to form polymeric structure, as in the capsules of some pathogenic bacteria and in few animal structures (Miyata et al 2006). Sialic acid-rich glycoconjugates are found in the zona pellucid of mammalian eggs and also in the jelly coat and vitelline layer overlying sea urchins eggs (Vilela-Silva et al 2008).…”

“…It was highly sulfated but differed from a similar molecule found in the egg jelly due to the occurrence of Neu5Ac instead of Neu5Glc and also due to very low proportion of other constituent sugars (Table 1). The sialic acid-rich polysaccharide from the sperm head had similarity with another glycoconjugate, named flagellasialin, which also contained Neu5Ac (Miyata et al 2006(Miyata et al , 2011. Studies on whether the sialic acid-rich molecule found in the sperm head interacted with the sulfated fucan from the egg jelly followed the analogy of the interaction of sulfated polysaccharides that regulated sponge cell-cell adhesion (Vilanova et al 2009).…”

“…In Hemicentrotus pulcherrimus and Strongylocentrotus purpuratus, this structure terminates with non-reducing end sulfated N-glycolylneuraminic acid (Neu5Gc) residues (Kitazume et al 1994. Miyata et al (2004Miyata et al ( , 2006 reported a polysialic acid on the flagella region of the sea urchins H. purcherrimus, S. purpuratus and S. franciscanus. This 8-Osulfated Neu5Ac, capped α-2→9-linked polyNeu5Ac-containing molecule, called "flagellasialin", seemed to be related with sperm motility, required for the fertilization.…”

“…Most sialic acids on the vertebrate cell surface participate in recognition and interaction events during the growth, development and immune response (Nasirikenari et al 2006;Nacher et al 2010). Sialic acids are rarely linked to each other to form a polymerized structure (Miyata et al 2006). Polysialic acids with the degree of polymerization ranging from 8 to 200 sialyl acid residues are found in few animals and some pathogenic bacteria capsules (Sato and Kitajima 2013).…”

Polysialic Acid Is Present in Mammalian Semen as a Post-translational Modification of the Neural Cell Adhesion Molecule NCAM and the Polysialyltransferase ST8SiaII

“…In contrast to vertebrates, however, also ␣2,9-and ␣2,5-O-glycolyl-linked polySia exist in addition to the ␣2,8-linked form. Kitajima and co-workers (31) show that polySia mediates important functions of sea urchin sperm. For instance, ␣2,9-linked polySia is suggested to influence the motility of sea urchin sperm, and ␣2,5-O-glycolyllinked polySia is discussed to potentiate the acrosome reaction (30).…”